STUDIES ON CHROMONE DERIVATIVES - REGIOSELECTIVE 1,3-DIPOLAR AND 1,4-CYCLOADDITION REACTIONS OF 3-CYANO-4H-1-BENZOPYRAN-4-THIONE

1,3-Dipolar cycloaddition reactions of 3-cyano-4H-1-benzopyran-4-thion e 1 with nitrilimines 3, nitrile oxides 7 and aldonitrones 8 yielded r egioselective cycloadducts involving the thione function. In the latte r two classes, the unstable cycloadducts fragmented to yield 3-cyanoch romone 11 and isothiocyanate 12 or thioamide 13, respectively. In cont rast, dienamines 14 preferred to react at the carbon-carbon double bon d in a 1,4-cycloaddition yielding xanthione (9H-xanthene-9-thione) 16 by elimination of HCN and the amine moiety.